Some modifications to ai::recall_result and ai::recruit_result:
1) Use check_recall/recruit_location() instead of the AI-specific checks in do_check_before().
2) Get rid of the redundant checks in do_execute().

An advantage of #1 is that the AI better supports sides with multiple leaders, along
with leader-specific recruit lists and recall filters (not full support, but better support).


git-svn-id: http://svn.gna.org/svn/wesnoth/trunk@56192 75b3775d-3801-0410-9e12-e2e43121521d